It has baffled scientists for decades - exactly what is the mystery 'third element' at the Earth's core?

Now, a Japanese team has the answer - and says its silicon.

Researchers have been searching to solve the mystery at the centre of our planet for decades after discovering there is something other than iron and nickel there.

Researchers have been searching to solve the mystery at the centre of our planet for decades after discovering there is something other than iron and nickel there.

THE EARTH'S CORE

The innermost part of Earth is thought to be a solid ball with a radius of roughly 1,200km (745 miles).

Too study it, researchers analyse how seismic waves pass through the region to tell them something of its make-up.

Previous studies have shown it is mainly composed of iron, which makes up an estimated 85% of its weight, and nickel, which accounts for about 10% of the core.

However, the final 5% has baffled them until now

Japanese scientists believe they have established the identity of a 'missing element' within the Earth's core.

Lead researcher Eiji Ohtani from Tohoku University told BBC News: 'We believe that silicon is a major element - about 5% [of the Earth's inner core] by weight could be silicon dissolved into the iron-nickel alloys.'

'We measured the sound velocity of iron alloy compounds at high pressure and temperature relevant to the Earth’s core,' the researchers wrote in their presentation for the Fall Meeting of the American Geophysical Union in San Francisco.

Eiji Ohtani and his team created alloys of iron and nickel and mixed them with silicon for the experiment, before subjecting them to the immense pressures and temperatures believed to exist in the inner core.